Low density resin composite of high stiffness

ABSTRACT

The present invention relates to a method of producing low density polydiene resins having high yield strengths and the products thereof. In particular a polydiene resin, such as dihydroxyl terminated 1,2-polybutadiene is reacted at room temperature with an organic chain extender, such as hexamethylene -1,6-diisocyanate, and a graft comonomer such as N-vinyl-2pyrrolidone in the presence of a peroxide free radical initiator, such as O,O&#39;&#39;-bis(t-butyl peroxy) diisopropylbenzene, whereby an elastomeric material having the peroxide and a graft comonomer dispersed therethrough is produced. At a subsequent period of time, the elastomeric material can be exposed to elevated temperatures whereupon the elastomer is cured to a low density resin having a high yield strength.

United States Patent 1 3,860,672 Lagally 1 Jan. 14, 1975 [5 LOW DENSITY RESIN COMPOSITE 0F 3,635,891 1/1972 Lubowitz et al. 260/859 R HIGH STIFFNESS 3,674,743 7/1972 Verdol et al. 1. 260/859 R Inventor: Paul Lagally, Annapolis, Md.

Assignee: The United States of America as represented by the Secretary of the Navy Filed: Apr. 12, 1974 Appl. No.: 460,420

References Cited UNITED STATES PATENTS 2/1969 Verdol et a1. 260/859 R 3/1969 Lubowitz 260/859 R 9/1970 Lubowitz et a1. 260/859 R 10/1971 Lubowitz 260/859 R Primary Examiner-Morton Foelak Attorney, Agent, or Firm-R. S. Sciascia; J. A. Cooke [57] ABSTRACT The present invention relates to a method of producing low density polydiene resins having high yield strengths and the products thereof. In particular a polydiene resin, such as dihydroxyl terminated 1,2- polybutadiene is reacted at room temperature with an organic chain extender, such as hexamethylene -l,6- diisocyanate, and a graft comonomer such as N-vinyl- 2-pyrrolidone in the presence of a peroxide free radical initiator, such as 0,0'-bis(t-butyl peroxy) diisopropylbenzene, whereby an elastomeric material having the peroxide and a graft comonomer dispersed therethrough is produced. At a subsequent period of time, the elastomeric material can be exposed to elevated temperatures whereupon the elastomer is cured to a low density resin having a high yield strength.

6 Claims, N0 Drawings LOW DENSITY RESIN COMPOSITE OF HIGH STIFFNESS BACKGROUND OF THE INVENTION This invention relates to polydiene resins and more particularly to polydiene resins having either urethane or epoxy groups.

For a variety of applications (e.g., deep sea buoyancy structures, aviation structures, etc.) low density plastic resins having high compressive yield strengths are needed. The state of the art teaches that functionally terminated 1,2-polybutadiene resins, which are chain extended with a diisocyanate or diepoxide, may exhibit a low density and a remarkable ultimate strength exceeding that of many other high strength plastic materials. However, these resins lack high yield strengths and high elastic moduli.

For example, resin composite obtained from dihydroxy 1,2-polybutadiene and toluene-2,4-diisocyanate had, after ring closure and/or crosslinking with a peroxide, a density of 1.04 and an ultimate compressive strength of 38,400 psi but a yield strength of only 5,500 psi and a compressive modulus of 225,000 psi. By comparison, a conventional epoxy resin had a density of 1.24, an ultimate compressive strength of 21,000 psi, a yield strength of 18,000 psi, and a compressive modulus of 500,000 psi. However, because conventional epoxy resins have high densities, they are less desirable for aviation or deep sea buoyancy structures than the low density polydiene resins. Therefore, it would be desirable to find novel low density polydiene resins having higher yield strengths than the prior art low density polydiene resins.

SUMMARY OF THE INVENTION Accordingly, one object of this invention is to provide novel low density polydiene resins.

Another object of this invention is to provide low density thermosetting polyolefinic resins having higher yield strengths.

A further object of this invention is to provide low density, high yield strengths, thermosetting resins having viscosity and cure characteristics suitable for the fabrication of castable plastic materials under the conditions of vacuum potting.

A still further object of this invention is to provide a method of manufacturing low density polydiene resins having higher yield strengths.

These and other objects of this invention are accomplished by providing a resin which is produced by contacting (A) a difunctional polydiene prepolymer having (1) two terminal functional groups selected from the group consisting of hydroxyl and carboxyl and (2) a predominant amount of vinyl groups on alternate carbon atoms of the polydiene backbone, with (B) a chain extender, provided that when the terminal functional groups on the polydiene are hydroxyl groups, the chain extender is a diisocyanate, but when the functional groups on the polydiene are carboxyl groups, the chain extender is a diepoxide, and with (C) a graft comonomer selected from the group consisting of N-vinyl-2- pyrrolidone, N-vinyl-3-pyrrolidone, N-vinylcarbazole, N-vinylimidazole, N-vinylpyridine, coumarone, indene, and mixtures thereof, at ambient temperature in the presence of (D) a peroxide free radical initiator to produce the reaction product. This reaction product can then be cured at elevated temperatures to produce the final polydiene resin.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The backbone of the resin of the present invention is formed either (1) by contacting a dihydroxy polydiene prepolymer with a diisocyanate as a chain extender to form a polyurethane polydiene resin or (2) by contacting a dicarboxy polydiene with a diepoxide to form an epoxy polydiene resin. Because of their greater yield strengths, the polyurethane polydiene resins are preferred over the epoxy polydiene resins.

The dihydroxy or dicarboxy terminated polydiene prepolymers used in the present invention should have a high residual vinyl or alkenyl content. Polydienes derived from isoprene, dimethylbutadiene, methylpentadiene, or butadiene are suitable, with dicarboxy 1,2 polybutadiene and dihydroxy 1,2-polybutadiene being preferred and dihydroxy 1,2-polybutadiene being more preferred. Dihydroxy and dicarboxy polydiene prepolymers having molecular weights of from about 600 to about 3,000 are preferred. If the molecular weight exceeds 3,000, the prepolymers become too viscous for proper casting and potting operations.

The chain extenders for the dihydroxy polybutadiene prepolymers may be aromatic as represented by toluene-2,4-diisocyanate or naphthalene-1,5- diisocyanate. However, the non-aromatic diisocyanates (e.g., hexamethylene-l ,6-diisocyanate, 2,2,4- trimethylhexamethylene-l,6-diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate) are preferred because they undergo urethane and allophanate formation rather slowly thus displaying low viscosities during the casting and vacuum potting operation. lsophorone diisocyanate is the more preferred chain extender.

The key feature of this invention is the'grafting of a cyclic monomer selected from the group consisting of N-vinyLZ-pyrrolidone, -N-vinyI-S-pyrrolidonc, N- vinylcarbazole, N-vinylimidazole, N-vinylpyridine, coumarone, indene and mixtures thereof onto the polymer backbone. The preferred graft monomers are N-vinyl-2-pyrrolidone, N-vinyl-3-pyrrolidone, and mixtures thereof.

Although the free radical initiator used is not a critical limitation, 0,0'-bis(t-butylperoxy) diisopropylbenzene works well as the catalyst. Preferably about 2 parts by weight of the free radical initiator should be used for every parts by weight of the dihydroxy or dicarboxy polydiene prepolymer.

The preferred range of the molar ratio of aliphatic diisocyanate to dihydroxy polydiene prepolymer is from about 0.75:1 to about 1.30:1, with from 0.95:1 to 1.10:1 being the more preferred range. For instance, preferably from 12 to 20 and more preferably from 15 to 18 parts by weight of isophorene diisocyanate chain extender (MW=222) should be used with every 100 parts by weight of dihydroxy 1,2-polybutadiene prepolymer (MW 1420).

If aromatic diisocyanates are reacted with the dihydroxy polydiene prepolymer, an excess of the aromatic diisocyanate should be used for proper viscosity control. Thus, the preferred range of the molar ratio of aromatic diisocyanate to dihydroxyl polydiene prepolymer is from about 0.95:1 to about 1.65:1, with from 1.20:1 to 1.50:1 being the more preferred range. For example,

preferably from about 12 to about 20 and more preferably from 15 to 18 parts by weight toluene diisocyanate chain extender (MW 174) should be used for every 100 by weight of the dihydroxy 1,2-polybutadiene prepolymer (MW 1420) used.

The preferred range of the molar ratio of the cyclic graft comonomer used in this invention to the dihydroxy or dicarboxy polydiene prepolymer is from about 0.60:1 to about 6.40:1 with from 4.45:1 to 5.75:1 being the more preferred range. For instance, from about to about 50, and more preferably from 35 to 45 parts by weight of N-vinyl-2-pyrrolidone (MW l l 1) should be used for every 100 parts by weight of dihydroxy 1,2- polybutadiene prepolymer (MW 1420). The amount of N-vinyl-Z-pyrrolidone which can be used for a given weight of prepolymer is limited by the hygroscopic properties of the vinyl pyrrolidone.

These cyclic graft comonomers are grafted onto an already existing polydiene polymer backbone and therefore are to be distinguished from polymers where the cyclic comonomers are part of the backbone itself.

The difunctional polydiene prepolymer, chain extender, cyclic graft comonomer, and free radical initiator are all mixed together and allowed to react at ambient temperature for about 1 hour. Later the reaction mixture may be poured into casts or structural spaces and cured at elevated temperatures.

Moreover, by embedding glass or phenolic microspheres into the reaction mixture before the curing step at elevated temperatures, syntactic buoyancy foams having superior strength and buoyancy characteristics are obtained. Note that before the curing step at elevated temperatures, the reaction mixture contains some unreacted isocyanate groups which have an inherent reactivity with silanol (or other metal hydroxide) groups located in the surface of the glass microspheres. The pyrrolidone moieties contribute further to the adhesiveness of the resin matrix. And finally, adhesion promotors derived from silyperoxides (e.g. tris(- tertbutylperoxy) vinyl silane) drastically increase bond strength and they reduce water absorption of the glass resin interface.

The following examples serve to illustrate the present invention without, however, limiting the same thereto:

EXAMPLE 1 To 100 parts by weight dihydroxy 1,2-po1ybutadiene having the properties:

: pyrrolidone. The viscosity rose from 350 to 1250 centi- TEMPERATURE (C) VISCOSITY (op) The product was poured into a mold and cured consecutively 48 hours at C plus 24 hours each at C, C and 200C.

The cured castings had the following strength characteristics:

Yield Strength (0.2% offset), psi 11800 Ultimate Strength. psi 27500 Compressive Modulus. psi 450000 Density (gr/cc). 1.04

EXAMPLE 2 Example 1 was repeated omitting the N-vinyl-2- poises at 90C over a period of 1 hour and the following strength characteristics of the cured resin were determined:

Yield Strength (0.2% offset), psi 7400 Ultimate Strength, psi 36000 Compressive Modulus, psi 367000 Density (gr/cc) 1.04

EXAMPLE 3 To successive portions of 200 parts by weight dihydroxy 1,2-polybutadiene having properties as described in Example 1, there were added 36 parts by weight toluene-2,4-diisocyanate and subsequently 10, 20, and 40 parts by weight N-viny1-2-pyrro1idone. Finally, 4 parts by weight 0,0-bis(t-butylperoxy) diisopropylbenzene was stirred into the mixture.

Castings made were cured consecutively 24 hours each at 90l 15C, l05l20C, and l20l40C. 1 2 The following table summarizes the compositions (in my ontent. a Hydroxy Content Meg/gr U9 parts by weight) and the strength characteristics of the Viscosity, poises at 45C 55 cured castings:

A B C D dihydroxy 1,2-polybutadiene 200.0 200.0 200.0 200.0 Toluene-2,4,diisocyanate 36.0 36.0 36.0 36.0 N-vinyl-2-pyrrolidone 0.0 10.0 20.0 40.0 Vul-Cup R 4.0 4.0 4.0 4.0

A B C D Compressive Yield Strength, 8100 9781 9970 1 1000 psi (0.2% offset) Ultimate Strength, psi 42000 28000 21000 25800 Compressive Modulus, psi 328000 331000 345000 385000 Density (gr/cc) 1.00 1.03 1.03 1.04

6 EXAMPLE 4 at from 100 to 110C, andfinally 24 hours at from Mixtures of dihydroxy ILPOWbutadiene, 120 to 200C. The syntactic foam thus obtained had isophoronediisocyanate, N-vinyl-2-pyrrolidone, triphyslcal Charactensucs as follows? methylolpropane trimethacrylate and 0,0-bis(t- (Sjpecifix Gravgy 0.552(34.4 pcl) 5 ompressive ydrostatic Strength, psi [4.900 butylpermfy) dlisopropylbenzene were prepared from Ultimate Compression Strength. psi IUHOO the followmg ahquot parts: 02% Offset Yield Strength. psi 9,800

A B c D E dihydroxy 1,2-polybutadiene 200.0 200.0 200.0 200.0 200.0 lsophoronediisocyanate 30.0 30.0 3010 30.0 30.0 N-vinyl-2-pyrrolidone 20.0 40.0 40.0 20.0 20.0 Trimethlolpropane Trimethacrylate 0.0 0.0 20.0 10.0 20.0 Vul-Cup R 4.0 4.0 4.0 4.0 4.0

v Compressive Modulus, psi 334 000 After m1x1ng, cast ng and curing as descrlbed in Ex Water Absorption (after [68 hours ample l, the followmg strength data were obtamed: 31900 psi)v percent A 13' c D E Yield Strength 7800 9700 10350 8400 9150 0.2% offset), Psi Ultimate Strength, psi 22000 17600 28400 31500 31000 Compressive Modulus, psi 339000 378000 437000 387000 400000 Density (g/cc) 1.04 1.04 1.04 1.04 1.04

EXAMPLE 5 What is claimed as new and desired to be secured by A syntactic foam buoyancy material was prepared by Letters Patent of the Unnefi States the maximum random packing of B-D hollow glass Process for producmg a cured polydenc rcsm microspheres (3M Company) in a mixture of a low 35 compnsmg; density prepolymer containing the modifiers. The basic Contactmg (A) dlhydroxy Polydlime havmg resin matrix consisted of 325 parts (by weight) dihytwo termma] hydYPXy groups-and a P droxy 1,2-polybutadiene, 49 parts isophorone diisocyaamount of 0Y groups ahmate Carbon nate and 13 parts 0,0-bis (tert-butylperoxy) diisoproatoms of h P l/ h b newtth (B) an orpylbenzene (commercially known as v pc 40 game cha1n extender which 15 a dnsocyanate, and used as vulcanizing agent. Modification for increased (C) graft COmPIlOmeT seleFted m the stiffness and interfacial bonding comprised 130 parts g p cQnslstmg of l Y 'PY U Q N'Y y vinylpyrrolidone, 65 parts trimethylolpropane trimeth- -py hq N-v y a az l N- 1 nyl lmldaZ- acrylate and 13 parts (tert-butylperoxy) vinyl silane. y -py d courmarone. indene a d After deaeration in a vacuum potter, the obtained mixtures thereof, 11 the pl'esencc N a P glass-resin composite w s S bmitt d to th f ll i 1de free rad1cal 1n1t1ator to produce an elastomenc cure cycle; 48 hours t 90C, 48 hours at 100 110C material having the perioxide and the graft comoand 24 hours at l20200C. The syntactic foam thus nomer dispersed therethrough substantially unre obtained had physical characteristics as follows: 50 acted, and then (11) curing the elastomer at elespecific Gravity 056N353 pd) vated temperatures to produce a firm resmous ma- Compressive Hydrostatic Strength. psi 16,200 terral. Ultimate Compressive Strength P {H33 2. A thermosetting polydiene resin comprising: g'gzf g g j gg iri g" 4271000 an elastomeric material which is the reaction product Water Absorption (after 168 hours) at ambient temperatures of (A) a dihydroxy polydi- 9000 ene prepolymer having (1) two terminal hydroxy EXAMPLE 6 groups and (2) a predominate amount of vinyl groups on alternate carbon atoms on the polydiene A syntacnc foam buoyance mater1al was prepared by b kb with (B) an organic chain extender h maxlmum random Packmg P 5 hollow glass which is a diisocyanate, and with (C) a graft comomlcrospheres p y) In a mlXtuYe a 10W nomer selected from the group consisting of density resin prepolymer contammg the mod1f1ers. The N i 1-2- ]id N i |-3 |i basic resin mat consisted Of 325 Parts y g vinylcarbazole, N-vinylimidazole, N-vinylpyridine, dihyd y 1,2-p0lybutadiene, 49 Parts ISOPhOFOIIe courmarone, indene and mixtures thereof, in the i506 anate a 13 Parts utylp y) resence of (D) a eroxide free radical initiator,

Y P P diisopropylbenzene. After deaeration a vacuum potter, the obtained glass-resin composite was submitted to the following cure cycle: 48 hours at C, then 48 hours provided that the peroxide and the graft comonomer are dispersed through the elastomeric material substantially unreacted.

the group consisting of N-vinyl-2-pyrrolidone, N-vinyl- 3-pyrrolidone, and mixtures thereof.

5. The product produced by the process of claim 1.

6. The product produced by the process of claim 3. 

2. A thermosetting polydiene resin comprising: an elastomeric material which is the reaction product at ambient temperatures of (A) a dihydroxy polydiene prepolymer having (1) two terminal hydroxy groups and (2) a predominate amount of vinyl groups on alternate carbon atoms on the polydiene backbone, with (B) an organic chain extender which is a diisocyanate, and with (C) a graft comonomer selected from the group consisting of N-vinyl-2-pyrrolidone, N-vinyl-3-pyrrolidone, N-vinylcarbazole, N-vinylimidazole, N-vinylpyridine, courmarone, indene and mixtures thereof, in the presence of (D) a peroxide free radical initiator, provided that the peroxide and the graft comonomer are dispersed through the elastomeric material substantially unreacted.
 3. A process according to claim 1 wherein the cyclic graft comonomer is selected from the group consisting of N-vinyl-2-pyrrolidone, N-vinyl-3-pyrrolidone, and mixtures thereof.
 4. A thermosetting resin according to claim 2 wherein the cyclic graft comonomer is selected from the group consisting of N-vinyl-2-pyrrolidone, N-vinyl-3-pyrrolidone, and mixtures thereof.
 5. The product produced by the process of claim
 1. 6. The product produced by the process of claim
 3. 